This invention relates to improvements in a high fatigue screw thread system.
When an external force is exerted on a bolt and a nut which are in threaded engagement with each other, the load born by the bolt is distributed to the respective contacting threads of the bolt, causing at each root a stress .sigma..sub.b in a degree corresponding to the load applied to each thread as well as a stress .sigma..sub.t corresponding to the axial clamping force of the bolt. In order to reduce these stresses to enhance the fatigue strength, it is necessary to disperse load distribution in the contacting portions while suppressing concentration of stress in the respective thread roots as little as possible.